1. Field of the Invention
This invention relates to valve tappets in internal combustion engines. More specifically, the present invention is an improvement in valve tappet design that eliminates many of the problems found in conventional valve tappets.
2. Description of the Related Art
It is well known to utilize roller tappets for valve actuation in internal combustion engines. These tappets allow increased engine speeds with less wear and energy dissipation. A typical roller tappet has a cylindrical body with a bifurcated portion at one end for receiving the roller and its associated shaft. The roller follows a cam causing the tappet to reciprocate in a bore of the engine block. The movement of the tappet controls the movement of an associated valve. In order to increase the flow of oil for adequate lubrication, conventional valve tappets have provided a centralized groove machined circumferentially into a portion of the tappet body. Such a tappet is disclosed in U.S. Pat. No. 4,809,651 issued to Gerchow.
There are several problems associated with conventional valve tappets of the type disclosed by Gerchow. FIGS. 1-3 illustrate a conventional roller tappet. Tappet 2' has body 4' and roller 10' as well as lifter rod seat 8'. The groove formed in the center of body 4' inherently defines edges 7 at its interface with the tappet body. This can be the source of scuffing of the lifter bore when the tappet is subject to typical side thrust loads. Also, because of the decreased diameter at the grooved portion of the tappet, the tappet structure is weakened and may bend in the bore when subject to extreme forces. This causes engine failure requiring that the engine block be disassembled in order to remove the bent tappet. Furthermore, the conventional tappet design does not always allow for adequate lubrication under extreme conditions because the oil can only pass on either side of central groove 5.